I've reported 'shall we go to Warsaw?'. This is quite a complicated topic, but I believe that in this particular case (without context, that is) the use of 'shall' is perfectly legit (denoting the proposition rather than a simple question). Last post here http://fluentli.com/questions/shall-we-go-to-the-cinema explains this quite nicely.
This distinction in Polish is achieved by intonation, isn't it?
Yeah, the problem is that "Are we going to Warsaw" is Present Tense* and "Are we going to go to Warsaw" is Future Tense.
*Yeah, of course its meaning may refer to the future, but as it works exactly the same way in Polish, we keep 'Present Tense in the future meaning' and 'normal Future Tense' apart. Because for a learner of Polish, it's not that obvious that "jedziemy" is Present Tense and "pojedziemy" is Future Tense.